In recent years, there has been proposed a technology in which user data (data of User-Plane) is directly communicated among a plurality of radio terminals without passing through a radio base station (D2D communication). The communication of user data directly performed among the plurality of radio terminals is performed by using a part of radio resources assigned to a mobile communication system. However, in the D2D communication, the communication of control data (C-Plane) is performed via the radio base station, similarly to a conventional mobile communication system.
Meanwhile, in the D2D communication, there exists a need of considering various methods as a method for assigning a radio resource to a transmission-side terminal and a reception-side terminal.